"These defendants made several statements about Mrs Trump that are 100% false and tremendously damaging to her personal and professional reputation," Mr Harder said in a statement.

"Defendants' actions are so egregious, malicious and harmful to Mrs Trump that her damages are estimated at $150m," Mr Harder's statement said.

He has filed the complaint before the Circuit Court for Montgomery County in the US state of Maryland.

Mrs Trump, 46, was born in Slovenia and moved to the US to work as a model in the 1990s. She married Mr Trump in 2005.

Blogger Webster Tarpley had written that Mrs Trump feared her past becoming public.

The article on the Daily Mail's website quoted claims published in Slovenian magazine Suzy that the modelling agency Mrs Trump was working for also functioned as an escort agency, court papers show.

The newspaper also quoted Slovenian journalist Bojan Pozar, author of an unauthorised biography, who claimed Mrs Trump had posed for nude photos in New York in 1995 and alleged that she had met Mr Trump that year, three years before their reported first meeting in 1998.

Her lawyers say she moved to the US in 1996.

Mr Tarpley meanwhile alleged that Mrs Trump was "reportedly obsessed by fear of salacious revelations by wealthy clients from her time as a high-end escort" and had suffered a "full-blown nervous breakdown".

The Daily Mail's retraction, published late on Thursday, insisted it had not suggested the sex work claims were true but said that, even if false, they could affect the US presidential campaign.

In July, Mrs Trump was embroiled in a row over plagiarism, after her speech at the Republican convention. Lines matched almost word for word those delivered by First Lady Michelle Obama at the Democrats' convention in 2008.

An employee of the Trump Organisation, Meredith McIver, later admitted her role in writing the speech, saying it was her mistake.